Succinic acid and its derivatives are widely used as specialty chemicals for applications in foods, pharmaceuticals, and cosmetics. Furthermore, succinic acid is a valuable 4-carbon intermediate useful for the production of 1,4-butanediol, tetrahydrofuran, and gammabutyrolactone.
Although the succinate ion is a common intermediate in the metabolic pathway of many organisms, there are no examples of any fermentation that produces succinate in large amounts or with high yields. For example, succinate is a key intermediate for anaerobic fermentations by propionate-producing bacteria, but it is only produced in low yields and in low concentrations.
Succinate is also produced by anaerobic rumen bacteria These bacteria include Bacteroides ruminicola (hereafter written B. ruminicola) whose growth and metabolism is described by Howlett, et al., Applied Environ. Microbiol., 32, 274-283 (1976) and Bacteroides amylophilus (hereafter written B. amylophilus) whose culture and growth are described by Caldwell, et al., J. Bacteriol., 98, 668-676 (1969) and by Hamlin, et al., J. Bacteriol., 72, 548-554 (1956).
Although the rumen bacteria give higher yields of succinate than do the propionate-producing bacteria, the reported fermentations were run in very dilute solutions and gave a variety of products in generally low yields. Moreover, the rumen organisms tend to lyse after a comparatively short fermentation time, thereby, leading to unstable fermentations.
In 1961, Anderson and Ordal isolated a facultative anaerobe, Cytophaga succinicans, which produced succinate, acetate, and formate from dextrose with fixation of carbon dioxide, J. Bact., 81, 139 (1961). However, this organism produced succinate in such low concentrations that it would not be economically feasible to recover succinic acid from the fermentation medium. Similar results were observed with the Bacteroides fragilis obtained from the gastrointestinal tract, Caspari, et al., Arch Microbiol., 135, 16-24 (1983).
In order for a process for the preparation of succinic acid to be commercially attractive it should produce succinic acid in high yields and at high concentrations. In addition, there must be a simple method for purification of the succinic acid.
We have now discovered a method for the anaerobic fermentation of carbohydrates to succinate in high yields and with high productivity. Furthermore, the succinate is produced in sufficiently high concentration in the fermentation medium to permit economical recovery of succinic acid by simple purification method.